A known image data generating device receives light from a subject through a light receiving device, which includes an array of photoelectric conversion elements, and detects the amount of light received from the subject for each photoelectric conversion element. The image data generating device arranges pixel values corresponding to the amounts of light received to generate plane image data representing the subject's plane image. Another known image data generating device generates distance image data by arranging a pixel value corresponding to the distance to a subject.
A known image data generating device for generating distance image data allows a light emitting device to emit light to a subject. One emission operation is accompanied by multiple light receiving operations during different periods. The light receiving operations cause the amounts of light received during different periods. Based on the amounts of light received, the image data generating device detects a phase difference between the light emitted to the subject and the light reflected from the subject to calculate a distance to the subject (e.g., see Patent Document 1).                Patent Document 1: JP-A-2006-516324 T (U.S. Pat. No. 6,906,302 B2)        
A known light receiving device mounted on such an image data generating device uses a CMOS circuit for generating a signal corresponding to a charge generated by the photoelectric conversion element.
Another known light receiving device is provided in the form of a combination of a CCD circuit and a CMOS circuit as its peripheral circuit. The CMOS technology is not suited for CCD circuits although the technology is indispensable to formation of peripheral circuits such as an ADC (analog/digital) circuit. The light receiving device using the CCD circuit requires an interface circuit or a companion chip between the CCD circuit and the peripheral circuit, complicating a manufacturing process. In addition, the CCD circuit consumes large power for driving.
Instead of the CCD circuit, the CMOS circuit can be used to extract a charge from a photoelectric conversion element and output a signal equivalent to the charge. This makes it possible to prevent a manufacturing process from being complicated and manufacture an economical, low-power consumption light receiving device. A distance image data device using the CMOS circuit has recently become widespread.
The light receiving device needed to generate distance image data can also generate general plane image data. A recently developed light receiving device has functions of not only generating distance image data but also generating plane image data.
As described in Patent Document 1, the known distance image data generating device provides a pair of floating diffusions for a photoelectric conversion element to detect a phase difference between emitted light and reflected light. Reverse phases are applied to a period of accumulating charge using a first floating diffusion and a period of accumulating charge using a second floating diffusion. After the light emitting device emits light, the first floating diffusion accumulates a charge generated by the photoelectric conversion element during the first period. The second floating diffusion accumulates a charge generated by the photoelectric conversion element during the second period.
This operation is repeated to allow the floating diffusions to respectively accumulate charges corresponding to the light incident on the photoelectric conversion element during different periods. Charges accumulated in the floating diffusions are converted into voltage values as output values. The output values are used to detect a phase difference between the emitted light and the reflected light and find a distance to the subject.
Thus, such a technique constructs and controls the light receiving device as mentioned above to find a distance to the subject. In contrast, when the technique uses the light receiving device to generate plane image data, however, a resolution of plane image data is limited to that of distance image data.
The above-mentioned technique provides one photoelectric conversion element with multiple floating diffusions. In addition, the photoelectric conversion element needs to be surrounded by sets of output circuits including transistors for charge transfer and output transistors for generating a voltage value corresponding to a charge accumulated in the floating diffusion. It is difficult to narrow an interval for laying out the photoelectric conversion element. When the common light receiving device is used to generate distance image and plane image data, the resolution for plane image data is therefore limited to be low.
Conventionally, the image data generating device may have functions of generating both distance image data and plane image data and use the common light receiving device. In such a case, it has been difficult to maintain a resolution of plane image data to be equivalent to that of a dedicated plane image data generating device.